In a photocoupler used in an environment at high temperature and high humidity, the sealing resin is required to have higher heat resistance and moisture resistance.
In a photocoupler in which the optical semiconductor element is sealed with resin, peeling and the like occurring at the resin interface of the double mold structure may degrade the reliability due to water absorption and oxidation.
Another problem is the change of optical coupling efficiency and the like by the change of optical intensity due to peeling and discoloration of the resin.